An inhibitor of the microsomal triglyceride transfer protein inhibits apoB secretion from HepG2 cells.

Abstract

The microsomal triglyceride (TG) transfer protein (MTP) is a heterodimeric lipid transfer protein that catalyzes the transport of triglyceride, cholesteryl ester, and phosphatidylcholine between membranes. Previous studies showing that the proximal cause of abetalipoproteinemia is an absence of MTP indicate that MTP function is required for the assembly of the apolipoprotein B (apoB) containing plasma lipoproteins, i.e., very low density lipoproteins and chylomicrons. However, the precise role of MTP in lipoprotein assembly is not known. In this study, the role of MTP in lipoprotein assembly is investigated using an inhibitor of MTP-mediated lipid transport, 2-[1-(3, 3-diphenylpropyl)-4-piperidinyl]-2,3-dihydro-lH-isoindol-1-one (BMS-200150). The similarity of the IC50 for inhibition of bovine MTPmediated TG transfer (0.6 ,iM) Genetic studies (1)(2)(3)(4) have demonstrated that an absence of microsomal triglyceride (TG) transfer protein (MTP) causes abetalipoproteinemia, a disease characterized by a defect in the assembly and secretion of apolipoprotein B (apoB) containing plasma lipoproteins. These studies indicate that MTP is required for the production of the apoB containing lipoproteins, very low density lipoproteins and chylomicrons by the liver and intestine. The requirement for MTP for lipoprotein production is further supported by studies using cell lines that are not of hepatic or intestinal origin. When a truncated form of apoB representing 53% of the full-length apoB-100 is expressed in HeLa cells, virtually no apoB is secreted (5). However, when MTP is coexpressed with apoB, apoB is secreted as a lipoprotein particle. Similar findings have been observed in COS cells (6).MTP is found in the lumen of microsomes isolated from liver and intestine (7). The protein purified from bovine liver is a heterodimer consisting of the multifunctional enzyme, protein disulfide isomerase, and a unique, large 97-kDa subunit (8-10). In vitro, MTP A mixture of compound A (62.5 mmol) and Zn dust (438 mmol) in AcOH (250 ml) was heated at reflux for 18 h, cooled to room temperature, filtered through Celite (Aldrich), and concentrated. The residue was dissolved in CH2Cl2 (500 ml), washed with saturated NaHCO3 (2 x 100 ml) and brine (100 ml), dried over MgSO4, and concentrated. The crude product was recrystallized from i-PrOH to yield 2,3-dihydro-2-[1-

The Hepatitis B Virus X Protein Inhibits Secretion of Apolipoprotein B by Enhancing the Expression of N-Acetylglucosaminyltransferase III

“…In addition, MTP, an intraluminal protein in the endoplasmic reticulum plays an essential role in regulating the assembly and secretion of apoB containing lipoproteins (44,50,56). It is interesting to note that HBx-and GnT-III-transfected cells showed down-expression of MTP mRNA but not in vectortransfected cell.…”

The Activity of Microsomal Triglyceride Transfer Protein Is Essential for Accumulation of Triglyceride within Microsomes in McA-RH7777 Cells

“…Physical interaction between MTP and apoB has been observed (13)(14)(15)(16)(17)(18)(19), but it is not clear if MTP also catalyzes lipid transfer onto apoB in vivo. Inactivation of MTP in hepatic or intestinal cells invariably impairs apoB assembly and secretion (7,20,21). On the other hand, coexpression of the MTP 97-kDa subunit with recombinant apoB facilitates assembly of small, dense lipoproteins containing apoB in heterologous cells (22)(23)(24)(25).…”

A Drosophila Microsomal Triglyceride Transfer Protein Homolog Promotes the Assembly and Secretion of Human Apolipoprotein B

“…MTP Inhibition-The MTP inhibitors BMS-200150 and BMS-197636 (Bristol-Myers Squibb) (33,34) were dissolved in Me 2 SO at concentrations of 10 and 2 mM, respectively. Final Me 2 SO concentrations were normalized in each experimental set of dishes and did not exceed 0.5%.…”